Fluidic Origami: A Plant-Inspired Innovation

The impulsive and recoverable movements in plants like the Venus flytrap have inspired scientists and engineers for more than a century. Even though the associated actuation mechanisms and physiological features of these movements have been relatively well studied, there have not been significant efforts to holistically apply the lessons from the plant kingdom to engineered multifunctional materials and structural systems. By combining the plant movement principles and paper folding topology, a novel adaptive structure concept called fluidic origami was invented in this research project. The idea is to combine different Miura-Ori sheets along their crease lines to form a three dimensional topology, which has naturally embedded tubular cells. Filling these cells with working fluid, one can strategically control their internal pressures and volumes to achieve multiple adaptive functions concurrently.

For example, fluidic origami can achieve distributed shape morphing according to the origami folding trajectory by actively changing the internal fluid volume (e.g. via pumping). Fluidic origami can also significantly tailor its stiffness properties by constraining the internal fluid volume via simple on-off valve control. In addition, fluidic origami structure is multi-stable, and the existence and shape of these stable configurations can be controlled by the fluid pressure. The performances of these unique adaptive functions are based on scale-independent geometric principles, and it’s highly programmable by tailoring the origami crease pattern.

Building upon these ideas, an integration of fluidic origami cells could lead to novel adaptive structures capable of distributed and rapid shape change based on the similar physical principles as the plant movements. Therefore, fluidic origami can have great potentials in various applications like high-performance morphing aircraft, kinetic architectures, and impulsive actuators.

Muscle: Inspiration for a New Class of Engineered Adaptive System

Skeletal muscle possesses several features – such as properties adaptability, multi-functionality, robustness, and versatility – that are attractive for a broad range of scientific and engineering applications. Much of the engineering research focus to date has been on emulating the whole-muscle characteristics, leading to advanced concepts for actuation and locomotion mechanisms, but there has been a scarcity of investigations that take inspiration from the synergistic assembly of skeletal muscle’s microscale and nanoscale active and passive mechanical constituents. This research aims to develop new adaptive engineered systems by exploiting a more complete understanding of the micro- and macroscale mechanical constituents and compositions of muscle.

The research objectives include developing an understanding of one-dimensional mechanical modules designed to emulate muscle’s nanoscale cross-bridge constituent, and exploiting modularity to assemble these modules into larger systems, similar to the assembly of muscle cross-bridges into sarcomere contractile units. Investigations inspired by the asymmetric potential energy landscape of cross-bridges, and by their remarkable ability to effectively store and release energy to enable sudden motions and reduce the energetic cost of periodic motions have shown that mechanical systems may be strategically designed to exhibit similar characteristics, and incorporation of these behaviors into multi-dimensional structural and material systems enhances opportunities for properties adaptation and energy capture and release. The results of this research are expected to foster the development of new structural and material systems exhibiting multi-functionality, properties adaptability, and improved energy dissipation and recovery.

Earthworm-Inspired Metameric Robot Locomotion

Earthworms possess flexible body and strong locomotion capability in various environments, which have inspired researchers and engineers to develop earthworm-like robots. It is revealed that the metameric segmentation, the antagonistic muscle layout, and the setae are three important morphology features for the earthworm to perform effective locomotion, and the retrograde peristalsis wave is the key locomotion mechanism that the earthworm takes. Much of the research to date has been on the design of segmented robots, with major focus on the actuation mechanisms. However, there has been a scarcity of efforts that are devoted to the understanding and utilization of the earthworms’ locomotion mechanisms. As a result, this research project aims to develop control methods for generic metameric locomotion robots by exploiting the correlations among robot segment coordination and locomotion performance, and the earthworm’s peristaltic waves.

Building upon the metameric feature of the earthworm-like robot, generic mechanical models of the metameric robot are built. Two methods are developed to control the robot segments for effective locomotion. From a bio-inspiration perspective, a generic gait generation algorithm is proposed by mimicking the earthworm’s basic locomotion mechanism. From a robotics perspective, the robot segment actuations are coordinated by making use of their symmetry relationship. These two approaches, although are significantly different, converges toward the same finding that the peristalsis wave is an inherent mechanism of earthworm-like locomotion and can be adopted to effectively control the metameric robot locomotion. The concept of metameric architecture as well as the proposed control methods will advance the state of the art of the design and control of crawling robots.

A Modular Metastructure Approach — Creating a New Paradigm of High Performance Structural Systems

Modular architectures are the foundation of numerous biological, atomistic, and advanced metamaterial systems. By such design, unique global functionality is obtained which is not possible by the constituent members alone, for example large shape change, reversible phase transformation, and guided-wave capability. Inspired by these architectures, this research aims to realize a metastructure concept for the macroscale to achieve extraordinary structural characteristics by building from modular structural “cells”. In contrast to systems developed from conventional materials and having limited abilities, metastructures will empower advanced global features, exceptional performance, and unprecedented functionalities, including adaptive mechanical properties, robust and reversible morphing, and embedded vibration and wave control features.

One example of our explorations is to seek the concept of creating engineered metastructures from the assembly of mechanical, metastable modules. The critical feature of the modular platform is the exploitation of multiple coexistent metastable states engendered via the strategic module design, and the multiplying nature of the coexistent states as metastable modules are assembled. In this study, one-dimensional metastable modules are created using a series configuration of springs/elasticities, where one is bistable and the other is monostable, (a) and (b). Parallel assemblies are created by stacking and constraining the modules at the housing ends using alignment rods while a common, rigid guide rod governs the resulting metastructure end displacement , Fig. (c). Fig. (d) illustrates the reaction force adaptation when a one metastable module of transitions from one to another metastable state. The research encompasses both the general theory and practical design of each metastable module and such modularity creates an accessible pathway to exploit metastable states for programmable metastructure adaptivity. Results of this research will represent a major leap forward in adaptive structures and material systems and introduce new concepts for phase-transition structures.

The main objective of this research is to advance the state of the art of Structural Health Monitoring (SHM) systems by creating novel Frequency Selective Structures (FSS) and an FSS-based Impediographic monitoring technique. The proposed approach is based on the concept of concurrent design where the SHM system is no longer retrofitted to an existing structure but, instead, it is designed concurrently with the structure itself. The system is achieved by implementing the idea of Frequency Selective Structure. FSS exploit the concept of mistuned periodic structures as a general framework to synthesize dynamically tailored components with self-focusing vibration energy capabilities. The new structural design approach will allow delivering targeted excitation to the damaged areas even in complex, non homogeneous components. The integration of FSS with the impediographic approach will then enable advanced damage identification capabilities characterized by high sensitivity, high resolution and a minimized transducer and sensory network.

If successful, this research will create a transformative intellectual pathway in synthesizing novel and realistic structural damage identification methods for complex mechanical systems. The technology will have general applicability and could be implemented across the aerospace, mechanical and civil engineering fields leading to the next generation of transportation and infrastructure systems having advanced health monitoring capabilities. The proposed technology will also eliminate the barriers that have prevented, to date, the experimental implementation and validation of the impediographic approach. Experimental findings will allow an unprecedented insight into impediography and provide critical inputs to foster its application to diverse fields, such as medical imaging, where remote non-invasive monitoring techniques are of primary importance.

Polymer-matrix fibrous composites such as those reinforced by glass or carbon fibers are increasingly prevalent in structural venues due to their high strength and low weight. However, fibrous composites are susceptible to delamination or failure by separation of fibrous layers. Left unchecked, delamination can propagate extremely rapidly and culminate in catastrophic structural failure. Structural health monitoring (SHM) is any method by which the integrity of a structure is continually assessed. SHM tailored for composites would greatly enhance standards of safe operation in composite structures through immediate structural identification. Nonetheless, SHM is far from ubiquitously implemented due to low sensitivity of sensors to damage and instable/non-convergent detection algorithms.

Carbon nanotube (CNT) fillers have recently been used to tailor the electrical conductivity of polymers that otherwise behave as insulators. The polymer transitions from insulating to conducting as CNTs are added to form connected and electrically conductive networks. Delamination severs connections between CNTs which manifests as localized changes in conductivity. Strain reorients and translates CNTs thereby degrading electrically connected networks resulting in changes in conductivity. Dependence of electrical diffusive properties on mechanical stimulation is known as piezoresistivity.

Electrical impedance tomography (EIT) is a method of imaging the internal conductivity of a domain using boundary measurements. In polymers which depend on CNT networks for electrical conductivity, delamination severs connections between the filler material causing local changes in conductivity. These conductivity changes can be imaged through EIT, and its ability to spatially locate internal conductivity changes with non-invasive measurements makes it well suited to damage detection in conductive composites.

This research advances state of the art SHM by coupling the piezoresistive properties of conductive polymers with EIT. The coupling process improves both stability/convergence and damage sensitivity for enhanced delamination detection in conductive composites.

Energy Harvesting via Bistable Snap Through Systems

The conversion of vibrational energy into electric power provides an opportunity to develop self-sufficient microelectronics or generate electricity in environments not amenable to other power sources or line transmission. For example, by feeding on wave oscillations, a deployment of field sensors may operate in an ocean environment even in the absence of solar or wind energy; likewise, a structural health monitoring system could be powered by the same vibrations that wear upon the structure over time. This unique potential initially stimulated studies that considered linear resonating “harvester” designs to convert the ambient vibration to power but has recently been extended to the study of bistable energy harvesting devices. Instead of a resonant effect, bistable systems exhibit a snap through dynamic of switching from one stable state to the other, yielding potentially high-displacement and high-velocity dynamics beneficial for the conversion of the kinetic energy into electric power. Snap through is inherently a non-resonant effect and as such can be excited by a wide range of forms and spectra of input vibrational energy, making bistable systems a more robust energy harvesting design than linear systems.

This research aims to critically understand the capability of bistable devices to serve as energy harvesters in realistic vibrational environments. The nonlinearities of snap through systems challenge preconceived notions regarding the dynamic trends to be encountered and necessitate careful investigation. A variety of rigorous analytical methods are employed to draw general conclusions about the dynamics of individual and coupled bistable systems and how to optimally design them for maximum energy harvesting performance. Corresponding experiments are conducted to validate the predictions and give evidence to the multitude of dynamics beneficial for energy harvesting from snap through systems. A wider impact of this research is the applicability of the results to fields like vibration control, vibration damping, sensing, and actuation. The thorough understanding of bistable snap through system dynamics is therefore hoped to significantly advance the state of the art for energy harvesting and similar fields.

Multi-Stable Chain for Ocean Wave Energy Conversion

This research aims to develop an alternative energy conversion principle and proof-of-concept hardware that resolves issues encountered when scaling down the direct-drive energy conversion techniques used by existing fixed-location, electric grid-integrated wave energy converters (WEC). The high eddy current damping inherent in driving the generators in such WEC makes the conversion principle highly inefficient for small systems and thus the potential for easily deployed and relocated marine power supplies is lost.

To surmount the limitations, this study explored the combination of vibration energy harvesting dynamics and phase transitions as inspired means to convert slow wave heaving motion into higher frequency oscillations. Through electromagnetic induction, the kinetic energy of the impulsively excited energy harvesting cells was converted and stored. Linking of the cells to induce cascading phase transitions was found to be more efficient in converting the motions to electrical energy than using an identical number of cells in parallel. Using frequency up-conversion principles, the serially-connected chain could also convert exceptionally low frequency input motions at 0.1 Hz just as effectively as isolated links converted higher frequency vibrational energy at 0.6 Hz. The preliminary findings demonstrate the potential for the energy harvesting chain as a viable means for portable and efficient marine wave energy converters.

Vehicle Load Estimation for Enhanced Vehicle Controls

Total vehicle load, including mass of occupants and drive resistance, has a direct impact on vehicle drivability and fuel economy. A recent development of a transmission torque sensor and an availability of on-board accelerometer open up a possibility of calculating total vehicle load in real time, accounting for vehicle mass and drive resistance. This research focuses on the development of a new methodology for accurately estimating total vehicle load in real-time based on transmission torque measurements and its application to vehicle controls for enhanced safety feature and fuel economy such as load (mass)-compensated collision warning (for enhanced safety) and load (mass)-compensated shift scheduling (for fuel economy).